Add recent up host count to the host summary

🗣 Description

Updates the host summary query to pull a count of hosts with a state of "up" and have had a vuln scan in the last 11 days.
Also updates the host summary model to store this value and the API to return this value to the frontend.

💭 Motivation and context

This new value is needed so it can replace the current scanned host count, as that value is already present elsewhere on the VS dashboard and is redundent.

🧪 Testing

API and storage tested locally. Query has been tested against redshift, but will need to be tested with the full redshift query in lz staging

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.